Processes of producing uranium hexachloride



Oct. 23, 1951 F. A. JENKINS 2,572,155

PROCESS OF PRODUCING URANIUM HEXACHLORIDE Filed July 15, 1943 Liquid Air 2/ To Vacuum Line Original Charge I Residue UC/ UC/ INVENTOR. Francis A. Jenkins ATTORNEY.

Patented Oct. 23, 1951 PROCESSES F PRODUCING URANIUM HEXACHLORIDE' Francis A. Jenkins, Berkeley, Califi, assignor to the UnitedStates of America asrepresented by the United States AtomicEnergy Commission Application July 13, 1943,-SerialNo. 494,447

7 Claims.

The present invention relates to U016 and processes of producing the same.

Heretofo're the compound U015 has not been known. Moreover, it'has been predicted th'at'the possibility of its production virtually negligible in view of its expected great instability. This view is entirely plausible since the 'tetrahalides of uranium form a series decreasing in stability in a regular-manner rrcm the fluoride through the chloride and the bromide to the iodide, and since 115 is extremely unstable. Thus it :has always been assumed that the hexahalide series of uranium terminates abruptly at the compound UF6YH The present invention .is predicated upon the discoveries that uranium ,pentachloride is a binary compound of the form UC14'UC1s rather thana monomeric compound of the form U015 and that in this compound the molecular bond may .be broken under certain conditions, producing as two independent com-pounds U014 and 11015. I

Accordingly, itisansobject of the'inve'ntion to provide ICU-d as a stable. compound.

Another objectoffthe invention .isto provide a process l'of ,producing IlCleaS a stable compound.

Another object of the invention is to providea process ,ofproducing UCls which utilizesuranium pentachloride. f hnotherobject o'fthe invention is to provide a prccess utilizing uraniuni pentachloride, whereby U014 I and U016 are produced. and separated. .Affurther object ofthe invention is to provide aprocess. in which the molecular-bond in the binary compound Tick-U016 is broken, whereby U014 ia'nd U015 -are produced as independent compounds.

h-further object ofthe invention is toprovide a process utilizing UCh-UCls, wherebyUCh and U016 are produced and U016 ,is .sublimed away from U014.

still further object of the invention is ,to provide a combinationheating and vacuum process of .p'roducing UCh and U016 from uranium pentachloride and of separating these products from each other.

'Ihe invention; both -as -.to 7 its organization and method of operation, together with further obf eets-and advantages thereof will best beunderstood byqreference to the following specification taken connection with the accompanying drawing, in=which+the-single figure is; aschematic illustration of 'Japparatussuitable for carrying out the processes of the present invention. lit-n accordance with -:the present invention, a

' suitable charge of uranium pentachloride (is placed :in a substantially conventional molecular still whichcomprises a hot surface heated in any suitable manner,such, forexample, as by a hot sand bath, and a coldsurfacecooled ;inrany;suitable manner, such, for example, as by liquid air. In the still the hot surface and the cold surface are disposed in spaced apart relation, and the space therebetween is. evacuated ;to an-extremely low pressure by suitable vacuum pumping ap paratus. -More particularly, ,the charge is placed on the hot surface of the stilland the temperature of the sand bath is suitably. controlled, "in order that the chargeds maintained at a [ternperature withinthe range to 0. Also, the amountof liguidairwhich-is applied to the cold surface of thestill issuch-thatthe tempera ture of the cold surface is maintained at 10 \.0. orbelow. Finally, the vacuum pumping apparatusisadjusted, so that the pressure within the still between the hot surface and the cold surface is maintained at Ya value between 10- and 10 mm. Hg. Preferably in carrying out the process, the space between the normalhotsurface and the normal cold surface-of the still is evacuated to obtain the subatmosphericpressure within the .range mentioned, before the normal hot surface is heated by the sand bath and the normal cold surface is cooled by the liquid air.

When the charge of uranium pentachloride is thus heated under subatmcspheric pressure, -it is converted into U014 andUCle, the .UCle being sublimed as it isproduced. The U0hremains-a's a residue upon thehot surfaceandthe sublimed U016 traverses the space between'thehot and cold surfaces to condenseuponthe coldsurfacein the form of iridescent, dark green, fine-grained crys* tals as the temperature or the charge isabove the sublimation point o'fU0ls andbelow the'sub-' surface. and the U016 sublimateris removed from v the cold surface. Ordinarilyin carryin aout the process a charge, of 100 grams of uranium penta chloride may be, substantially completelypeconverted into. a, residue:.oflUGlr-randua' sublimatesof UCIG in approximatelylthree hours.

use in vacuum apparatus, in that it has a verymuch greater vapor pressure at a considerably lower temperature than other volatile chlorides of uranlum, such, for example, as U014.

While the process may be carried out at a temperature below the lower end of the preferred range, it is noted that in the event the temperature is much lower than 80 C. the yieldof U016 from the charge is extremely poor and very slow. Similarly, while the process may be carried out at a temperature above the upper end ofthe preferred range, it is noted that in the event the temperature is much higher than 180 0-. the U014 produced as a residue in the charge itself begins to-sublime, and theUCls is decomposed to U01; and Clz before it can be sublimed from the hot surface. In other words, it. is essential that the process be carried out under conditions such that-the newly formed U016 is removed from the hot zone, or regionof maximum temperature, before any substantial decomposition of the product U016 can take place. Also, when the temperature is much higher than 180 0., the sublimate is of very low chemical purity in that large amounts of-U0l4 are mixed with the U016, and furthermore the yield is low.

Of course the vapor pressure-temperature curves of UCIG and U014 are of usual form, the vapor pressure increasing disproportionately with temperature, whereby there is a negligible sublimation of U014 within the normal sublimation temperature range of U016. However, for practical purposes of obtaining correspondinglyreasonable yields, it may be-said that the sublimation temperature of U016 is well below that l Decomposition of UCIQ begins. V 1 Pressure of U014 below 300 0. is negligible.

I Examples When the process is carried out employing a charge of uranium pentachloride, UCh-UCls, it

is believed that the molecular bond is broken, whereby U014 and U016 are produced as'independent monomeric compounds, and that the UCIB is sublimed away from the U014, as it'is noted that the sublimation-temperature of UC16 is considerably below that of U014 and that U010 has a much higher vapor pressure at a given temperature than U014. Further, it is thought that the following specific reaction takes place:

Theoretically, one mole of the binary compound UCh-UCls (831 grams) should yield one mole of the monomeric compound U014 (380 grams) and one mole of the monomeric compound UCIG (451 grams); the weight percent of chlorine in the residue U014 should be 37.34; and the weight percent of chlorine in the sublimate U016 should be 47.19. "The analyses of the residue and the sublimate produced: incident to carrying out the present process checked very closely with the theoretical values indicated. For instance, in a typical run utilizing a charge of 100 grams of uranium pentachloride, when the process is substantially complete analyses have indicated. a weight of U014 residue of 47 grams, a weightof U016 sublimate collected of .52 grams, and. a weight of U016 sublimate lost of one gram. Also, analyses for total uranium and total chlorine, made gravimetrically by tested procedure, indicatedthe following for the sublimed material:

Per cent Total U a 53.30 Quadrivalent U (2.31), Chlorine 46.41"

' v, 99.71 Atomic ratio Cl/U 5.85

When allowance is made for the inevitable decomposition which accompanies any transfer of material, except under vacuum in thoroughly baked-out apparatus, the analyses are so close to that required for UCIG that therecan be noserious doubt that the sublimate is substantially chemically pure U016; the atomic ratio 0l/U 015.85 obtained fro the analyses is well within experimental error of the" theoretical atomic ratio V 0l/U of 6. Also, analyses of the residue yield an atomic ratio of 0l/U of 3.94, clearly indicating that the residue is substantially chemically pure U014.

In further evidence of the fact that the binary compound uranium pentachloride. is converted into the two monomeric compounds mentioned, it is pointed out that check runs in the still under the conditions specified, utilizing the residue U014 and .the sublimate UCIG, yield very interesting results. More particularly, in a check' run utilizing the residue U014, thereis virtually no sublimate, indicating that the residue is already substantially chemically pure U014. On the other hand, in a check run utilizing the sublimate U015, there is virtually no residue, indicating that the sublimate is already substantially chemically pure U016. I I Preferably, the uranium pentachloride employed as a charge in the still in carrying out the present process is produced by the improved process disclosed in the copending application of Horace R. M-cCombie, Serial No. 506,336, filed October 15, 1943. More particularly, it has been found that when the charge of uranium pentachloride is produced in accordance with the process disclosed in the above mentioned McCombie application as contrasted with other known processes,'the yield of U013 from the charge in the still is considerably higher, and of'the order of 50% greater.-

if i f i I Referring now more particularly to the single figure of the drawing, there is illustrated asubstantially conventional molecular still which is suitable for carrying out the present process, the still comprising lower and upper casing members II and I2, respectively, formed of Pyrex glass. The lower casing member II is provided with an outwardly directed sealing flange I3 adjacent the upper end thereof, and the upper casing member I2 is provided with an outwardly directed sealing flange I4 adjacent thelower end thereof, the sealing flanges I3 and It being adapted to mate to provide a hermetic seal between the lower and upper casing members II and I2, respectively, of the still. The upper casing member I2 is provided with a re-entrant portion I5 projecting into and spaced inwardly from the side wall of the lower casing member II, in order to define a vacuum space between the lower and upper casing members II and I2, respectively. The lower casing member I I is provided with a bottom end wall I6, constituting a normally hot surface adapted to receive a charge I! of uranium pentachloride; and the re-entrant portion I5 of the upper casing member I2 is provided with a bottom end wall I8 constituting a normally cold surface. The bottom end wall I6 of the lower casing member II is arranged within a hot sand bath I9, whereby the charge I! is heated; and the re-entrant portion I5 of the upper casing member I2 is adapted to contain a body 20 of liquid air, whereby the surface I8 is cooled. Finally, the lower casing member II has a conduit 2I formed integrall therewith and communicating with the vacuum space disposed between the lower and upper casing members II and I2. The conduit 2| is suitably connected to vacuum pumping apparatus, not shown, and includes a stopcock 22.

In the operation of the molecular still, the charge I? of uranium pentachloride is first positioned on the normally heated surface I6 of the lower casing member II, the upper casing member I2 is brought into relation, and the flanges l3 and I l are appropriately sealed. The pumping apparatus is started, and the stopcock 22 is opened, whereby the pressure in the vacuum space between the lower casing member II and the upper casing member I2 is lowered to a pressure of the order of 10 to 10- mm. Hg. The temperature of the sand bath I9 is suitably adjusted, whereby the temperature of the charge I! is maintained within the range 80 to 180 C., and the body of liquid air is poured into the re-entrant portion I5 of the upper casing member I2, whereby the cold surface I8 is suitably cooled to a temperature of the order of 10 C. or below. When the charge I! is thus heated, the conversion takes place, whereby the charge I! of uranium pentachloride is progressively converted into U014 and UCle, the UCls subliming as it is produced and traversing the space between the hot surface I6 and the cold surface I8. Th UCl-i remains as a residue upon the hot surface I6, and the sublimate UCls is condensed to its solid state upon the cold surface I8. After the process has been completed, the stopcock 22 is closed and the still is removed to the dry cabinet and opened, as previously explained. It will be noted from the foregoing that, since the UCls is sublimed or vaporized substantially as it is produced [apparently by the disruption of the molecular bond of the uranium pentachloride (UCl4.UCle)l it is not permitted to remain in the hot zone for a time sufiicient to cause any substantial degree of thermal decomposition thereof, thus insuring maximum production and recovery of UCls as such.

Reconsidering the properties of the monomeric compound UCls, it is again noted that this product is of fine crystalline structure, having an iridescent dark green color. The vapor pressure of the product UCIe is of the order of 1 to 3 mm. Hg at 0.; and the product is extremely hygroscopic and unstable in ordinary atmosphere. When the product U016 is subjected to normal atmosphere containing moisture, it rapidly decomposes to UOzClz. However, the product UCls exists in stable form in dry air, nitrogen, helium, and other inert gases.

The vapor of UCls readily attacks most of the ordinary metals considerably more actively than does the vapor of U014, decomposing to U014. For example, UCls vapor at 100 C readily attacks copper, copp'er alloys, silver, iron, graphite, etc., and exhibits no substantial attack upon stainless steel, monel metal, nickel, and gold. The product UCls is soluble in water, decomposing immediately to UOzClz, and cannot be dissolved in ionic oxygenated solvents without decomposition to UO2C12. Finally, the product UCls is readily soluble in C014, producing a dark brown solution.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The process comprising heating uranium pentachloride to a temperature which is sufliciently high to convert it to UCl4 and UCls and which is above the sublimation temperature of U016 and below the sublimation temperature of U014, said heating being conducted under conditions such that the UCls which is produced is sublimed as it is formed, and recovering the UCls thus produced.

2. The process comprising heating uranium pentachloride to a temperature which is sulficiently high to convert it to U014 and UCle and which is above the sublimation temperature of UCls and below the sublimation temperature of UCh and simultaneously subjecting it to a pressure not appreciably greater than 10 mm. Hg, said heating being conducted under conditions such that the UCls which is produced is sublimed as it is formed, and recovering the UCle thus produced.

3. The process comprising heating uranium pentachloride to a temperature within the range 80 to C. and simultaneously subjecting it to a pressure not appreciably greater than l0 mm. Hg, whereby UCls is produced and sublimed substantially as it is formed, and recovering the [T016 thus produced.

4. The process comprising heating UCl4-UCle to an elevated temperature and simultaneously subjecting it to a subatmospheric pressure, whereby UCh and UCls are produced, subliming the UCle away from the U014 under conditions such that the UCls is removed from the heated zone before any substantial decomposition thereof takes place, and recovering the UCls thus produced.

5. The process comprising heating UC14'UC1G to an elevated temperature and simultaneously subjecting it to a subatmospheric pressure, whereby U014 and UCls are produced, subliming simultaneously to heat and a subatmospheric pressure in a heated zone, whereby UC14 and UCls are produced, subliming the UCls as it is produced, conducting the sublimed UCls away from the heated zone to. a remotely. disposed cooled zone, condensing the sublimed U016 to its solid state in the cooled zone, and recovery the UCls thus produced.

'7. The process comprising converting uranium pentachloride to U014 and UC'lc by heating it to "8 a tempratu're Within the-irange 80" to 180 C. while subjecting it to a pressure not appreciably greater than 10* mm. Hg, subliming the UCls,

conducting the sublimed UCls substantially as it is formed-away from the U014 to a remotely disposedcooled zone, and condensing the sublimed UCls to its solid state in the cooled zone.

1 Y F. A. JENKINS.

REFERENCES crrEn The following references are of record in the file of this patent:

Chemical Abstracts, vol. V, 1911, page 3772, Otto *Rufl and Alfred Heinzelmann, Danzig Z. Anorg. Chem. '72,"pages 63-84.

Mel1or,--C0mprehensive Treatise on Inorganic and Theoretical-Chemistry, vol. XII, 1932, pages '3 5, 83, and '84. (Copy in Division 59.) 

1. THE PROCESS COMPRISING HEATING URANIUM PENTRACHLORIDE TO A TEMPERATURE WHICH IS SUFFICIENTLY HIGH TO CONVERT IT TO UCL4 AND ULC6 AND WHICH IS ABOVE THE SUBLIMATION TEMPERATURE OF UCL6 AND BELOW THE SUBLIMATION TEMPERASTURE OF UCL4, SAID HEATING BEING CONDUCTED UNDER CONDITIONS SUCH THAT THE UCL6 WHICH IS PRODUCED IS 